I had a similar situation with a single new bird I was trying to integrate. We fenced off part of the run for her and let her sleep in the coop in a wire dog crate. We did this for almost three months, they still would not accept her. And this was a perfectly healthy, normal hen, but she was a single new bird, they just fixated on her and it just never worked out. They did eventually get to where she could free range near them in the pasture but they never allowed her in the coop. No way my husband was building another coop either so I finally just went to Tractor Supply and bought a cheap little chicken coop made by Ware, put it in my barn and that became her home. She slept there at night and free ranged my pasture and barn during the day, somewhat with the others. Interestingly one of my bantams from the other flock took notice and moved in with her shortly after and they became buddies. Crazy things. But it solved the immediate problem and there was peace for all of us once again. Oh and that was the LAST time I ever attempted to integrate a single newbie! Never again! Now I do groups of no less then three, and preferably more, with these same older chickens with no trouble.
